So after last week's seemingly irrevocable Keen-Reddington split—you know, the bit right after she discovered that he was framing her husband as some sort of two-timing Ruskie murderer—what on earth could ever bring these two back together on the same crime-fighting team? Try a mad research scientist setting off chemical bonds around the greater Washington area. Because that's the sort of thing that would convince me to let bygones be bygones.

The mad scientist is a chap named Frederick Barnes, and after a lifetime of merely designing chemical weapons for other people, he's apparently decided to cut out the middleman and set them off himself. The reason? His son is dying of a rare radiological disorder, so Dr. Barnes figures that if he infects enough people—or at least enough people who don't have the temerity to die right away—he can eventually find a cure. You know, when you say that scheme out loud, it sort of sounds crazy.

I guess Dr. Barnes never said it out loud because he sets off a couple of bombs during the course of this episode until he finds a single victim who doesn't contract the dread disease. So after taking some of her bone marrow—really, he's just borrowing it, honest—Dr. Barnes is about to inject his son with an experimental cure. That's when Keen catches up to him and—after being suitably chastened for letting Barnes slip away when she voluntarily surrendered her weapon—conducts an experiment of her own to see how Dr. Barnes reacts to being injected with sudden bursts of lead. Hypothesis: Not well. So the day is saved and the bad guy is brought to justice, and sorry, kid, but it looks like you won't be getting that cure for your disease after all, since we had to shoot your old man. Sorry about that.

On the domestic front, Tom and Lizzie seem to have patched things up from their earlier I Think You Might Secretly Be a Terrorist spat and have moved on to remodeling their home, a situation more fraught than any FBI interrogation, let me tell you. Reddington's doing some remodeling of his own, re-purchasing what is apparently the house that he used to live in with his family before embarking on a decades-long life of crime. Naturally, he burns it to the ground. Most new homeowners just repaint.

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Our story begins on the DC Metro, easily my favorite subway system within these continental United States. (My least favorite? The T in Boston, which trails just behind being dragged by a rope through the streets). A dapper, well-dressed gent makes his way onto the train, and eagle-eyed viewers will recognize him as Robert Sean Leonard, most recently of House, but I never watched that show, and I’m an old, tired man, so you’ll forgive me if I think of him as the overwrought aspiring actor from Dead Poets Society.

Anyhow, the nice, young lady sitting next to him on the train starts chatting him up after she notices that he’s wearing the same sharp-looking cap that she bought her old man. And the fact that Robert Sean Leonard reacts to this new like, "Oh shit, you have a family with hopes and dreams?" is telling that something quite dreadful is about to happen. There’s some more small talk where Robert Sean Leonard inquires if she sees her father often and seems cheered by the fact that she goes to church with her dad every Sunday. ("Oh, so you are at peace with your maker, then? It’s an innocent question that people ask in everyday conversation because life is so fleeting and precious!"). And soon the train has reached Robert Sean Leonard’s stop and he’s bounding off the Metro without his briefcase, which is probably just as well, given that it’s emitting a weird chemical cloud. Soon everyone on that train -- including the nice, young lady -- is hacking and coughing and ends up quite dead. On the bright side, that’s a few more members for that Poets Society Robert Sean Leonard is so fond of. On the down side, I could have done without the lingering, pre-credits shot of the dead kid. That’s entertainment, amirite?

Off to a place that’s only a slight improvement over a subway car filled with deadly chemical gas -- the Keen household. Lizzie has decided to kick off the kiss-and-make-up portion of their relationship by remodeling their dining room. As would you if someone planted a box falsely implicating your husband as a crafty international assassin instead of the milquetoast schoolteacher he apparently is. Also, Megan Boone’s wig is particularly distracting. It looks like something a Founding Father would wear while drafting the Articles of Confederation. Before she can really roll up her sleeves and look into the merits of assorted paint swatches, though, Ressler’s on the phone suggesting she may want to get up to speed on this chemical attack happening on the other side of town. Thirty-seven people are dead -- no survivors on the train. But the twitchy FBI IT guy who I guess is becoming a recurring character has noticed closed-circuit footage of Robert Sean Leonard entering the station with a briefcase but leaving without it. So we have our suspect: Robert Sean Leonard, the notorious poet serial killer.No, no, no. That would be stupid.